__________________We're on an express elevator to hell... going clown.HELLO, MY FRIEND - freindship make a happiness double times and divide sadness half and make us remove our unhappiness.
Some days you just can't get rid of a bomb

Some similarities:
- Little Willy himself looks like the hero of Crystal Caves with his gray skin and yellow hair.
- The gameplay is similar in that you have to grab all items before you can exit the level.
- You shoot rockets.
- The title screen moves the same.
- You choose which level you want to play in the same way.

The creator of Secret Agent, Peder Jungck, did license his graphics routines as the ProGraphx Toolbox to other developers. The toolbox is used in the Apogee games Crystal Caves, Dark Ages and Duke Nukem 1. It's also used in FBI Fred.

I was looking for other games that might use the ProGraphx Toolbox by searching for games that have data files with a size of 8064 bytes, when I found Little Willy. But alas, the file formats are different.